The present application claims priority to Taiwan application No. 089109978 entitled xe2x80x9cMulti-wave-reflector antenna dishxe2x80x9d filed on May 24, 2000.
1. Field of the Invention
The present invention relates to the structure of an antenna dish and more particularly to a multi-wave-reflector antenna dish, which has a minimal dish surface and simultaneously receives signals from a plurality of satellites, at fixed angles from each other; and related manufacturing techniques.
2. Description of the Related Art
In general, based on the fact that a direct broadcast satellite (DBS) is a point-to-multipoint, a ground receiver is capable of receiving signals directly from synchronized satellites by means of a small receiving antenna, a tuner device and household equipment. The process of transmission via satellite is as shown in FIG. 1, wherein program signals, digital audio as well as video, are transmitted with precision to an orbiting synchronized satellite 15 by manipulating an up-link antenna dish (transmitting antenna) 10. After individual users receive downlink signals transmitted by the satellite 15 through the antenna dish 20 and select desired satellite programs using a panel control on the satellite TV receiver 25, video and stereo audio signals are separated and played on the TV set 30.
FIG. 2 shows each component of the antenna dish 40 for receiving satellite signals with precision. The receiving antenna dish 40 comprises a parabolic reflector 42 for receiving and having satellite signals concentrated on the focal point. In addition, a LNBF (low noise block with integrated feed) module is installed on the parabolic reflector 42 to convert incoming radio frequency signals into intermediate frequency signals and send said signals to the tuner. Waves parallel to the axis of the parabolic reflector 42 are reflected by the reflector and concentrated on the focal point where the LNBF module 44 is positioned. Note that LNBF module 44 comprises a waveguide antenna 46 to receive microwave signals on the front end thereof and a circuit system 48 to process the signals on the rear end thereof. Furthermore, in addition to noise filtering, the LNBF module 44 also amplifies received signals from the parabolic reflector 42 to an acceptable scale for processing.
It should be noted that the conventional antenna dish 40 as shown in FIG. 2 is a circular parabolic antenna. Accordingly the equation of the aperture thereof can be expressed as X{circumflex over ( )}2+Y{circumflex over ( )}2=4fz, wherein f refers to the focal length of the circular dish.
Provided that the LNBF module is positioned at the only focal point of the circular dish and the reflector is orientated to the desired satellite, the said antenna is ready for reception and demodulation of the signals. As a result of the strong concentrating character of the focal point on the circular dish, the LNBF module 44 on the focal point receives signals with extremely high S/N (signal to noise) ratio. This significantly enhances reception. In other words, in conventional antenna designs, the strong concentrating character of the focal point on the circular dish contributes to gain raise, lower spillover loss and a better quality of received signal.
On the other hand, it is also the same strong concentrating character at the focal point on the circular dish that suppresses gain from unfocused waves and generates a considerably lower gain than it does from the axis of the circular dish. Therefore, when LNBF module 44 positioned at a non-focal point on the focal plane, the received S/N ratio is noticeably lower than that when LNBF module 44 is positioned at the focal point. In other words, a circular antenna dish can only receive signals from a targeted satellite and is not capable of receiving signals from other satellites. If one wants to receive signals from any other satellites using the same antenna dish, the orientation and the angle of elevation have to be readjusted in order to bring the axis of the paraboloid reflector 42 parallel to signal waves from other satellites, to concentrate the signal waves on LNBF module 44. There are alternatives to receive signals from a plurality of satellites such as installing several antenna dishes, but these alternatives are costly and require a large area.
It is noted that the quantity of communication satellites for transmitting various programs has continued to grow with the rapid development of communication satellite systems. From a user""s perspective, the capability to simultaneously receive programs broadcast from several satellites on a single antenna dish saves both cost and space. It is also more convenient and practical for users.
The objective of the present invention is to provide a multi-wave-reflector antenna dish that simultaneously receives signals from a plurality of satellites, at fixed angles from each other.
Another objective of the present invention is to provide an antenna dish that simultaneously receives signals from a plurality of satellites by integrating a reflector and a plurality of LNBF modules.
One other objective of the present invention is to provide an antenna dish having a reflector with a super ellipse projected aperture. This enables the reflector to raise gain and cut spillover loss at a non-focal point by minimizing the cross area of the antenna.
The present invention provides a multi-wave-reflector antenna dish that simultaneously receives signals from a plurality of satellites at fixed angles from each other and relevant design techniques. The antenna dish comprises a reflector with a superquadric projected aperture and a plurality of LNBF modules. The reflector is formed by projecting a superquadric on the paraboloid, projected aperture cutting and surface distortion of the aperture based on the generalized diffraction synthesis technique. Surface distortion involves required condition values such as radiation pattern, gain, and sidelobe level. Repeat computations are then conducted based on these variables, accordingly, to form a reflector that simultaneously focuses signals from different satellites on the LNBF module with the same radiation pattern and gain.